CVS bug: merge includes same lines twice, doesn't mark conflict

[Ken Ballou]

I believe I have found a bug in the CVS merge algorithm, as demonstrated
by the attached sample files.  There are three versions of a file named
"bug": revision 1.1, revision 1.2, and revision 1.1.2.1 (branch named
"branch").  If the working revision of the file is 1.2, the command "cvs
update -jbranch bug" correctly reports a conflict in the merge. 
However, the resulting file has two copies of the rule to make target
"cleanest", and there are no merge conflict indicators!

This is a heavily trimmed example of a merge problem we had with a much
larger makefile.  This is the smallest example I could create that
demonstrates the problem.

The attached compressed tar file contains the following four files:

  bug-1.1       revision 1.1 of file "bug"
  bug-1.2       revision 1.2 of file "bug"
  bug-1.1.2.1   revision 1.1.2.1 of file "bug"
  showbug       bash shell script to reproduce this bug

This bug was found in CVS version 1.11.1p1 on a RedHat-7.3 i686 system. 
I have verified it is also present in CVS as compiled from the CVS
sources available from the anonymous CVS server on Dec. 9.

Thank you.

                                        - Ken

bug.tar.gz
Description: GNU Zip compressed data